Low signal swing buffers or driver circuits, meaning circuits that provide an output signal that is used to control other downstream circuits or components, are an emerging technique to reduce dynamic power consumption in digital circuits. They achieve a dynamic power reduction by driving a load capacitance by an upper voltage swing that is smaller than a full rail power supply voltage, VDD. However, a low signal swing on an interconnect line can cause circuit failures if the signal does not develop sufficient voltage margin to the trip point of downstream gate(s). As a consequence, there is a need to be able to control the voltage swing to meet specific applications and provide an acceptable noise margin, or equivalently an acceptable signal margin.
Prior art circuits have addressed this need but have shortcomings. For example, one circuit uses a level shifter/receiver that is source coupled to achieve a low signal swing, and this results in a conductive input. Conductive inputs result in power dissipation, cause capacitors to discharge, and can't be used in dynamic circuits. Another circuit does not have any external control mechanism, which prevents the circuit from being specifically tuned. Another circuit describes controlling a voltage output swing in every cell with a set of discrete discharge transistors in that same cell, that are enabled by a set of digital control signals. However, this circuit requires several digital control signals to set the voltage level, and the circuit overhead is too high for standard applications. Yet another circuit describes the direct control of output voltage through control of the regulated power supply voltage of the driver circuit.
The present invention is illustrated by way of example, and its not limited by the accompanying figures, in which like references indicate similar elements. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Also, the functions included in the flow diagrams do not imply a required order of performing the functionality contained therein.